Sunday 4 December 9:30 2011

Mum runs full-pelt into the brickwork. Then her boy pushes the luggage trolley into the wall. Click, flash – he's gone, replaced by five French teenagers, arguing over who gets to hold the handle. They vanish and a middle-aged man steps up to snap the "Platform 9 3/4" sign. The queue behind him is 15 people long. Click: Harry Potter did this 10 years ago. Flash: we can too.

This is one of the weirder ways that JK Rowling's story endures. Half a baggage cart bracketed sloppily on to a brick wall, protected by a small green shed tucked to one side of King's Cross station. There's a security camera and a No Smoking sign. A McDonald's across the road. None of this stops people from queuing up to pretend they're heading to Hogwarts.

Wednesday 6 July 2011

Crowds gather for the Harry Potter and the Deathly Hallows Part 2 world premiere at Trafalgar Square on July 7, 2011 in London, England. Photograph: by Jon Furniss/WireImage Celebrities

It's the day before the Harry Potter and the Deathly Hallows –Part 2 premiere. We think we're in the dying days of a $7.7bn franchise. "It's insane," says the friendly PR woman of an event that will see 20,000 Potter fans crowd into central London to say goodbye to the world's biggest film series. "It's basically taking over Trafalgar Square – big screens, stage, everything." How does she plan to get the stars safely into the Leicester Square cinemas for the premiere? "Secret," she says, with a coy smile. She's happy with the mystique. The walkthrough's over – nearly time for the real thing.

Tomorrow David Thewlis will be standing, hunched a little, blinking a lot, on stage in Trafalgar Square, where 20,000 Harry Potter fans will be screaming – at him, at each other, at The End. Thewlis will wave and smile and wonder at the novelty.

"It's totally not intimidating," he says of the fans' reaction, shortly after the friendly PR woman drops him off for his interview. "You just look at it with a big smile. You're giggling inside." This, for Thewlis, is a bit of fun. Another chance to hang out with his castmates. Other than that, the Potter films, in which he played Remus Lupin off-and-on since 2004's The Prisoner of Azkaban, don't mean too much to him. "It's not been a big part of my life, to be honest," he says. "I don't feel like it's the end of a big era for me personally – it's not like I grew up with the Harry Potter films. It's been a job for the past eight years."

David Thewlis as Remus Lupin in Harry Potter and the Order of the Phoenix

Thewlis did Potter so he could work with HP3 director Alfonso Cuarón – "Amazing … Prisoner of Azkaban looks like an arthouse movie at times." – and do something else, such as The Lady and The Inner Life of Martin Frost and Veronika Decides to Die. The Potters kept him in the minds of producers ("You can just go and make independent movies for ever and no one sees them, then you're in danger of fading from view") and prompted a younger audience to watch his work. He had a laugh with Julie Walters ("one of my heroes") and felt like part of a family, but he won't miss it too much. "You can create an illusion where you think it's all the actors think about," he says. "To millions of people Harry Potter's who you are."

Thursday 7 July 2011

Emma Watson at the premiere of the last Harry Potter film Photograph: Dipasupil/FilmMagic

Sunday 5 December 2011, 13:00

"That's enough." Middle-aged Dad is growling at the young couple in front of him. He wants them to stop posing in front of the King's Cross installation so that his son – grizzling and impatient – can take his turn at the trolley. "That's ennn-nough."

Wednesday 6 July 2011

"Upstairs," says Gambon, sitting in the newly opened St Pancras Renaissance hotel the day before the premiere, "they want hand impressions."

"Hand impressions?"

"They want you all to give hand impressions. They put it in the sticky goo. And then you turn it over for a while. And they fill it with something and they have them on display at Leavesdon. But I said no because my hands are huge. They haven't got …"

"You've big hands, Michael."

"Yes. They've got rubber gloves, but there's no rubber glove big enough to fit me. So I said: 'No! I'm not doing it!' So I haven't done it. So I'm in the bad books."

Today Gambon is playing a role he's had off-and-on for nearly eight years – the Harry Potter cast-family's caring, sincere godfather. He seems genuinely sorry that, come next March, the Making of Harry Potter tour will lack bronze replicas of his very long mitts. He remembers his time on the films (as the Hogwarts headmaster, taking over from Richard Harris after his death in 2002) fondly, but it's a challenge to think of anything he has learnt from them. He's not particularly enamoured of the slow pace of big-budget film-making, but loves to see the result of all that "mucking about" on screen. ("You can't believe that what you're watching is something you took part in.") He speaks fondly of Daniel Radcliffe, Rupert Grint and Emma Watson, the young stars who grew up with the franchise. He's engaged and humble, respectful to the work. But he's a notorious scamp, a bit of a joker and a big mystery, all told. A Bafta award-winning veteran of more than 50 films who says he has a "real deep fear" of the camera ("worried about costing money for the film going through it") and is still at his best as a sidekick. Best guess? He's with Thewlis: Potter was a fun job, an interesting experience. Nothing life-changing.

Tuesday 5 July 2011

Harry Potter fans at the world premiere of Harry Potter And The Deathly Hallows, Part 2. Photograph: Danny Martindale/WireImage Celebrities

Wednesday 6 July 2011

"I'm nine years into this now," says Jason Isaacs. "Yet when I meet people who are shaking or in tears or who proclaim love for Harry Potter, I don't know what they're proclaiming love for. Is it the stories? The characters? Their journey? I'm not quite sure what it is that they're so in love with – but they're overwhelmed by it."

Jason Isaacs as Lucius Malfoy in Harry Potter and the Goblet of Fire

Isaacs, who starred in Potters two, four, five, seven and eight as Lucius Malfoy, talks eloquently and forcefully about HP. He's a preacher, an ambassador and a guard, describing the films with a passion that undermines the silly-funny things cynics say about them. He's a salesman though, as he'll say many times, nobody needs him to sell a ticket to Harry Potter. Potter is unique, unmatchable: "Everything else I've ever done, I wouldn't really mind if it hadn't been broadcast," he says. "I did it because it was a personal journey and I enjoyed the act of creation. And yet with Harry Potter there's something else going on that I can't quite put my finger on." Potter saves too: "In such a complicated world [it] gives unalloyed pleasure to so many people".

It's tricky to see what's behind the patter. He's "heartbroken" that it's over, but in the pre-interview small talk he was "heartbroken" to have lost his phone too. He's not a phony, but he is dramatic. And prone to superlatives. He was "given guardianship of something special", but you sense he really kept coming back for the same prosaic reasons as Thewlis and Gambon – it was a chance to have fun working with his favourite actors, for a couple of months every other year.

"I just want to say the biggest thank you to the 3,000 people who have been here for five nights in the pouring rain. You're the reason we've kept going and tried to make these films better and better and better." – director David Yates at the Harry Potter and the Deathly Hallows, part 2 premiere.

"Oh my God ... You know, maybe I'll just write another one." – JK Rowling at the Harry Potter and the Deathly Hallows, part 2 premiere

Sometimes the doors are shut. I guess so a cleaner can go in to sweep up the fag butts and scrub graffiti. During these fallow periods people still stand and wait, staring at the sign that says "Harry Potter is closed for essential maintenance". "Will he back soon?" asks an anxious tourist. Put money on it.